add body font-size

assets/sass/_theme/design-system/typography.sass

@@ -55,6 +55,7 @@ body
     font-family: $body-font-family
     -moz-osx-font-smoothing: grayscale
     -webkit-font-smoothing: antialiased
+    font-size: $body-font-size
     font-variant-ligatures: common-ligatures
     text-rendering: optimizelegibility
     line-height: $line-height-base